If Atheists do not believe in God..then why do they have such a spiritual interest and hang in R/S ?

It's for conversation. Being an atheist, I speak from experience: we like to argue and test people. We also like to broaden our interest in the subject so that we're ready for opposing argument and can form our own. Atheists (the ones that I know, including myself) tend to be annoyed, angry, or irksome when it comes to religion, and we enjoy attacking it, and the only place to do that is where there are conversations about religion.